83,884 research outputs found
A First-Principles Study of the Electronic Reconstructions of LaAlO3/SrTiO3 Heterointerfaces and Their Variants
We present a first-principles study of the electronic structures and
properties of ideal (atomically sharp) LaAlO3/SrTiO3 (001) heterointerfaces and
their variants such as a new class of quantum well systems. We demonstrate the
insulating-to-metallic transition as a function of the LaAlO3 film thickness in
these systems. After the phase transition, we find that conduction electrons
are bound to the n-type interface while holes diffuse away from the p-type
interface, and we explain this asymmetry in terms of a large hopping matrix
element that is unique to the n-type interface. We build a tight-binding model
based on these hopping matrix elements to illustrate how the conduction
electron gas is bound to the n-type interface. Based on the `polar catastrophe'
mechanism, we propose a new class of quantum wells at which we can manually
control the spatial extent of the conduction electron gas. In addition, we
develop a continuous model to unify the LaAlO3/SrTiO3 interfaces and quantum
wells and predict the thickness dependence of sheet carrier densities of these
systems. Finally, we study the external field effect on both LaAlO3/SrTiO3
interfaces and quantum well systems. Our systematic study of the electronic
reconstruction of LaAlO3/SrTiO3 interfaces may serve as a guide to engineering
transition metal oxide heterointerfaces.Comment: 50 pages, 18 figures and 4 table
Evaluation of semiconductor devices for Electric and Hybrid Vehicle (EHV) ac-drive applications, volume 1
The results of evaluation of power semiconductor devices for electric hybrid vehicle ac drive applications are summarized. Three types of power devices are evaluated in the effort: high power bipolar or Darlington transistors, power MOSFETs, and asymmetric silicon control rectifiers (ASCR). The Bipolar transistors, including discrete device and Darlington devices, range from 100 A to 400 A and from 400 V to 900 V. These devices are currently used as key switching elements inverters for ac motor drive applications. Power MOSFETs, on the other hand, are much smaller in current rating. For the 400 V device, the current rating is limited to 25 A. For the main drive of an electric vehicle, device paralleling is normally needed to achieve practical power level. For other electric vehicle (EV) related applications such as battery charger circuit, however, MOSFET is advantageous to other devices because of drive circuit simplicity and high frequency capability. Asymmetrical SCR is basically a SCR device and needs commutation circuit for turn off. However, the device poses several advantages, i.e., low conduction drop and low cost
Fluctuations of Entropy Production in Partially Masked Electric Circuits: Theoretical Analysis
In this work we perform theoretical analysis about a coupled RC circuit with
constant driven currents. Starting from stochastic differential equations,
where voltages are subject to thermal noises, we derive time-correlation
functions, steady-state distributions and transition probabilities of the
system. The validity of the fluctuation theorem (FT) is examined for scenarios
with complete and incomplete descriptions.Comment: 4 pages, 1 figur
Nitrogen doping of TiO2 photocatalyst forms a second eg state in the Oxygen (1s) NEXAFS pre-edge
Close inspection of the pre-edge in oxygen near-edge x-ray absorption fine
structure spectra of single step, gas phase synthesized titanium oxynitride
photocatalysts with 20 nm particle size reveals an additional eg resonance in
the VB that went unnoticed in previous TiO2 anion doping studies. The relative
spectral weight of this Ti(3d)-O(2p) hybridized state with respect to and
located between the readily established t2g and eg resonances scales
qualitatively with the photocatalytic decomposition power, suggesting that this
extra resonance bears co-responsibility for the photocatalytic performance of
titanium oxynitrides at visible light wavelengths
Designing interaction for a multi-touch wall
As large-scale display and multi-touch technologies become more affordable, the market has seen the development of multi-touch walls. This new medium offers a unique mix of information density, direct interactivity and collaboration support, and the new features have radical effects on interaction design. Here we explore some research issues together with proposed solutions and some design suggestions, based on our own approach to three areas of interaction design: multi-touch input, user interface and co-located collaboration
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